Hexane and propene fully penetrate within the micropores of the Fe-MFI zeolite and strongly adsorb. Decane, tetradecane, isooctane and toluene have a very limited access to the micropores and probably adsorb at the micropore mouths where then can act as reducing agents for NO. Linear alkanes (C6–C8), isoheptane and toluene have an easy access to the micropores of the mordenite MSM-20. Henry constants, adsorption enthalpies and entropies have been estimated. Pre-adsorbed carbon dioxide inhibits adsorption of propene and hexane on the Fe-MFI.